1. Field of the Invention
The present invention relates to ink jet recording on a recording medium, such as paper or cloth, and, in particular, to refreshing and recovering ink discharge in an ink jet recording apparatus.
2. Description of the Related Art
Recording apparatuses, such as printers, copying machines and facsimile apparatuses, record images consisting of dot patterns on recording media, such as paper, cloth or thin plastic films, on the basis of image information.
Depending on the recording method, such recording apparatuses can be classified into ink jet type apparatuses, wire dot type apparatuses, thermal type apparatuses, laser beam type apparatuses, etc. An ink jet apparatus records by ejecting ink (recording liquid) from ejection ports of the recording head so as to cause the ink to adhere to the recording medium.
Recently, various types of recording apparatuses have come into use. The most useful of such apparatuses comply with various requirements, such as providing high-speed, high-resolution, high image quality and low-noise recording.
With that in mind, ink jet type recording systems have been attracting attention because they are very quiet. In particular, an ink jet type recording system utilizing bubble jetting of liquid (hereinafter referred to as xe2x80x9cBJxe2x80x9d) by heating has been attracting attention as a high quality and inexpensive high-speed printing method readily allowing an increase in recording density, being very quiet and readily enabling color printing.
Further, because they increase recording speed, recording apparatuses having a recording head with a plurality of recording elements (hereinafter referred to as a xe2x80x9cmulti headxe2x80x9d) have come into general use. Further, to cope with various requirements of color recording, a recording apparatus having a plurality of such multi heads has been developed.
FIGS. 6(a) and 6(b) are perspective views of an example of a conventional ink jet recording head used in a typical ink jet recording apparatus. As shown in these drawings, this ink jet recording head includes: an orifice plate 21c having ink discharge ports (orifices) 21b; a grooved top plate 23 having grooves 10 forming ink passages (nozzles) communicating with the orifices and a common liquid chamber 13 forming an ink accumulator; and a heater board 16 having heat generators 22 provided in the ink passages and consisting of electro-thermal converters serving as heat energy generating elements for generating heat energy to be utilized in creating bubbles and ejecting ink from the orifices. Numeral 21a indicates an ink supply port leading to the common liquid chamber 13 and the ink passages.
An ink jet apparatus equipped with such an ink jet head has a cap used in a suction recovery operation, in which ink is sucked through the discharge ports in order to eliminate defective ejections. The cap also serves to prevent ink from drying in the discharge ports. As ink is being repeatedly ejected during recording, some bubbles in the ink passages may fail to disappear. If too many bubbles remain in the ink passage, or if the volume of the bubbles becomes so large as to block the nozzle outlets, it will become impossible to ensure passage of ink through the ink supply passages. The suction recovery operation mentioned above is often performed for the purpose of removing such bubbles.
An ink jet recording apparatus having a plurality of recording head, for example, a color ink jet recording apparatus having recording heads respectively corresponding to four ink colors, black (Bk), cyan (C), magenta (M) and yellow (Y), is provided, for example, with four suction/shutdown caps and four suction pumps respectively connected thereto, or a single large suction pump connected to all four caps. In such an ink jet recording apparatus, all of the different colored inks may be sucked simultaneously. In a type of ink jet recording apparatus which has a single suction pump, a single cap exclusively used for sucking, and shutdown caps for the recording heads, the suction of the inks in the recording heads is successively effected from head to head.
Conventionally, when performing a suction recovery operation, a cylinder pump has been used, which pump utilizes, instead of the gravitational force of the ink, piston movements, thus enabling the ink to be reliably recovered. This cylinder pump utilizes the surface of its piston when opening or closing a hole through which waste ink is recovered from an ink receiving member such as a cap, and causes the waste ink to be moved, by way of a waste ink transfer passage provided on the piston rod, to a waste ink container having a larger capacity for storing ink than the ink receiving member.
A color ink jet recording apparatus of the type in which a plurality of recording heads are successively sucked by using a single suction cap and a single suction pump, has a problem in that inks of different colors can be mixed in the suction cap when sucked therein, so that such mixed ink can be drawn into a nozzle, resulting in a mixed colored ink being printed on the recording paper.
To copy with this problem, preliminary ink ejection is performed in order to drain any mixed ink in the nozzle. However, to completely drain the mixed ink in the nozzle, the preliminary ejection has to be performed a number of times, which uses excessive ink and takes a long time.
Further, it is known that some of the solvent contained in the ink may evaporate from the ends of the nozzles, resulting in density inconsistencies at the start of the printing. To solve this problem, ink discharge by suction or pressurization is performed when printing is to be performed for the first time after a long shutdown period in order that such density inconsistencies may be mitigated. Further, an ink refreshing operation, such as preliminary ink ejection, can also be performed at a position and timing which do not interfere with the recording.
Further, wiping is performed in order to completely remove any ink remaining on the ejection face of the head after completion of an ejection recovery operation based on suction and pressurization and to remove any ink mist that has settled on the ejection face during and after printing. During this wiping operation, which is performed with a single wiper, some of the ink on the wiper can be transferred to the discharge port and mixed with the ink therein. To remove the resulting mixed ink, it is necessary to perform a discharge operation as in the case when preventing density inconsistencies. Thus, when a single wiping mechanism is used for a head using inks of different colors, inks of different degrees of lightness may be mixed with each other, making it necessary to perform an additional discharge operation in order to eliminate density inconsistencies caused by the recovery operation.
Such additional discharge can be effected, for example, by always performing a recovery operation, such as preliminary ink ejection or suction, whenever printing is performed, independently of how printing has been performed by the apparatus up to that moment. Alteratively, the recording apparatus may be provided with a timer for counting non-printing periods including power-off periods. In that case, a recovery operation is conducted whenever the time counted by the timer exceeds a predetermined length of time. Further, it is also possible to divide the time to be counted by the timer. That is, when the shutdown period has been short and a relatively slight evaporation on ink is expected, the recovery operation consists of preliminary ejection only. When the shutdown period has been long and the density inconsistencies cannot be easily eliminated by such ejection alone, ink discharge is effected by suction and pressurization. When the timer is used in this way, it is possible to attain a reduction in the amount of ink consumed since only preliminary ejection, which consumes a relatively small amount of ink, is conducted in the case where a slight amount of ink has been evaporated.
However, in a case when the ink in the head is extremely concentrated, a great amount of ink has to be consumed in order to remove such concentrated ink and to mitigate density inconsistencies, even when the above-described conventional ejection recovery techniques are adopted. Similarly, when preliminary ink discharge is performed for the purpose of preventing color mixing, a large amount of ink must be consumed for purposes other than printing before an amount of ink large enough to prevent density inconsistencies can be discharged.
According to a conventional method, to curtail the amount of waste ink, a preliminary discharge operation is interrupted simultaneously for all of the heads. That is, according to this conventional method, a temporary interruption of ink discharge is effected after a first stage of ink discharge, thereby enabling different portions of ink in the head to be uniformly mixed by eddy currents generated as a result of the ink flow in the head during preliminary discharge. After this, a second stage of ink discharge is executed, thereby eliminating density inconsistencies more effectively.
If, in the above conventional method, the discharging of ink is resumed before the ink concentrated through evaporation of solvent has been sufficiently mixed with newly supplied ink, a sufficient cleaning effect cannot be obtained, and a reduction in the amount of ink discharged cannot be achieved. Further, if the first stage of ink discharge is too long, a lot of time is required to perform the recovery operation.
One aspect of the present invention proceeds from the discovery that the optimum ink discharge interruption period varies for different heads, inks, etc., particularly in a color recording apparatus. Whether density inconsistencies in a color recording apparatus are conspicuous or not depends upon the lightness of the ink. For example, in the case of a recording apparatus using four colors, yellow, cyan, magenta and black, a relatively long ink discharge interruption period is necessary for yellow since density inconsistencies are liable to be conspicuous in this color. In contrast, black requires a very short interruption period since density inconsistencies in this color are not very conspicuous due to its low lightness.
A general object of the present invention is to provide an ink jet recording apparatus in which the length of a recovery operation can be reduced, so that the amount of waste ink and the time required for the recovery operation are reduced, thereby attaining a reduction in operating cost and an increase in throughput.
In accordance with one aspect of the present invention, an ink jet recording apparatus having a plurality of recording heads for respectively ejecting through discharge ports a plurality of inks of different lightness and a recovery mechanism for performing a recovery operation on a selected recording head by sucking ink through the discharge ports of the recording head comprises scanning means for moving each of the plurality of recording heads to a position facing the recovery mechanism, selection means for selecting one of the recording heads on which the recovery operation is to be performed, and recovery control means for performing the recovery operation successively on the plurality of recording heads in a descending order of ink lightness.
In accordance with another aspect of the present invention, an ink jet recording apparatus having a plurality of recording heads for respectively ejecting through discharge ports a plurality of kinds of inks and a recovery mechanism for performing a recovery operation on a selected recording head by sucking ink through the discharge ports of the recording head comprises scanning means for moving each of the plurality of recording heads to a position facing the recovery mechanism, ink ejection means for repeatedly ejecting ink from the discharge ports of a selected recording head, selection means for selecting one of the recording heads on which the recovery operation is to be performed, and ejection control means for controlling the number of times that ink is to be ejected from a selected recording head on which the recovery operation has been performed according to the kind of ink used by a preceding recording head on which the recovery operation has been performed.
In accordance with a still further aspect of the present invention, a recording head recovery method for an ink jet recording apparatus having a plurality of recording heads for respectively ejecting through discharge ports a plurality of inks of different lightness, a recovery mechanism for performing a recovery operation on a selected recording head by sucking ink through the discharge ports of the recording head and an ink ejection mechanism for repeatedly ejecting ink from the discharge ports of the recording heads comprises the steps of selecting a recording head on which the recovery operation is to be performed, performing the recovery operation on successive recording heads in order of descending ink lightness by bringing each of the plurality of recording heads successively to a position where they face the recovery mechanism, and ejecting ink from each recording head a number of times according to a preceding the recording head on which the recovery operation has been performed.
In accordance with a yet further aspect of the present invention an ink refreshing method for an ink jet recording apparatus having a plurality of recording heads for respectively ejecting inks of different lightness and an ink supply system for supplying the inks to the recording heads as the inks are ejected therefrom comprises the steps of initially discharging ink from discharge ports of a selected recording head, interrupting the initial discharge step for a predetermined period in accordance with the lightness of the ink discharged by the recording head, wherein the period is longer for inks of greater lightness, and subsequently discharging ink from the discharge ports of the recording head after the interruption.
In accordance with a still further aspect of the present invention, an ink refreshing method for a recording apparatus having a recording head for ejecting from discharge ports a given amount of ink and an ink supply system for supplying ink to the recording head as the ink is ejected therefrom comprises the steps of initially discharging ink from the discharge ports by applying energy to ink in the recording head or to the storage member or to the supply system, interrupting the ink discharge for an appropriate one of a plurality of periods set in accordance with an ascending order of the amount of ink ejected from the recording head, and subsequently discharging ink from the discharge ports after the interruption by applying energy to ink in the recording head or to the storage member or to the supply system.